1. Field of the Invention
The present invention relates to a hyperbranched polyol macromolecule having both primary and secondary hydroxyl groups as part of the structure thereof, and also including a branched hydrocarbon chain to give flexibility to the polymer. More particularly, the present invention relates to a hyperbranched polyester polyol macromolecule, of the type described, which is usable to form high-solids coating compositions; to a method of making the macromolecule, and to coating compositions made therewith.
2. Description of the Background Art
Certain hyperbranched macromolecules are known for use in preparing high-solids coating compositions.
U.S. Pat. No. 5,418,301 to Hult et al. teaches a dendritic macromolecule which is formed beginning with a central initiator molecule having reactive hydroxyl groups thereon. A monomeric chain extender is attached to each of the reactive hydroxyl groups to form a highly branched structure. A chain stopper molecule may, optionally, be added to the chain extender to further increase the size of the macromolecule, and to terminate the macromolecule-forming reaction.
U.S. Pat. No. 5,663,247 to Sorensen et al. discloses another hyperbranched polyester macromolecule, formed from an epoxide nucleus and hydroxy-functional carboxylic acid chain extenders, and a method of making the hyperbranched macromolecule.
Other polyesters are disclosed in U.S. Pat. Nos. 5,852,162 and 5,869,191.
Some coating compositions formed with the known hyperbranched macromolecule have a tendency to crack when they are flexed. Such relatively brittle materials are less than optimal for use in making coating compositions which are intended to be applied to automotive bodies or flexible materials, such as resiliently bendable plastics or elastomers. Since modern engineering often combines dissimilar materials such as, e.g., metal and plastics or elastomers into an assembled product to be painted, a need exists for coatings which are useful to paint all of such dissimilar materials.
Although the known hyperbranched macromolecules are useful for their intended purposes, a need still exists in the art for an improved hyperbranched macromolecule having engineered properties which allow formation of coating compositions which are both durable and flexibly resilient.
The present invention provdes a hyperbranched polyester polyol macromolecule having a plurality of both embedded and exterior hydroxyl groups with a branched hydrocarbon chain for flexibility thereon.
A hyperbranched polyol in accordance with the invention, generally, includes
a) a central nucleus comprising a hydrocarbon structure with a plurality of oxygen atoms;
b) a first chain extension attached to the central nucleus, the first chain extension being formed from a compound comprising a carboxyl group and a plurality of hydroxyl groups;
c) an intermediate substituent attached to the first chain extension, the intermediate substituent being formed from a compound selected from the group consisting of polyfunctional carboxylic anhydrides and acids thereof; and
d) a second chain extension attached to the intermediate substituent, the second chain extension comprising a hydroxyl group and being formed from a flexible hydrocarbon compound having a terminal or non-terminal epoxide group thereon.
A particularly preferred starter polyol for use in the present invention is trimethylol propane. A preferred intermediate substituent for attaching to the first chain extension is a cyclic anhydride or acid thereof, most preferably an alicyclic anhydride or acid.
The present invention also encompasses a method of making a hyperbranched polyester polyol. A method in accordance with the invention, generally, includes the steps
a) reacting a polyol with a first chain extender, which contains a plurality of hydroxyl groups and also contains a carboxyl group, to form a first generation branched core;
b) optionally, further reacting the first generation branched core with the first chain extender, to form a subsequent generation branched core;
c) reacting the first or subsequent generation branched core with a compound selected from the group consisting of carboxylic anhydrides and acids to form an ester bridge therewith, thereby forming an intermediate polyester macromolecule; and
d) reacting the intermediate polyester macromolecule with a second chain extender having a terminal or non-terminal epoxide group in a flexible hydrocarbon chain thereon, to form a hyperbranched polyol having both primary and secondary hydroxyl groups thereon.
Hyperbranched polyols which are products of the above method exhibit the low viscosity needed for coatings operations.
Accordingly, it is an object of the present invention to provide a method of making a hyperbranched polyester polyol having both exterior (primary) and partially embedded (secondary) hydroxyl groups in the structure thereof.